"The man was taken into custody and has undergone a mental health assessment — he has since been sectioned under the Mental Health Act and remains in the care of medical professionals," London's Metropolitan Police said on Sunday, December 26. "Enquiries into the full circumstances of this incident are being progressed by Metropolitan Police Specialist Operations."
According to the police, officers were on the scene around 8:30 a.m. local time.
Thames Valley Police Superintendent Rebecca Mears said the suspect, a 19-year-old man from Southampton who apparently had a crossbow with him, did not enter any buildings.
"The man has been arrested on suspicion of breach or trespass of a protected site and possession of an offensive weapon," Mears said. "We do not believe there is a wider danger to the public. He remains in custody at this time. We can confirm security processes were triggered within moments of the man entering the grounds."
Police apparently informed the monarch, 95, of the security breach, and it's been reported that Prince Charles, Camilla, Duchess of Cornwall, Prince Edward and his wife, Sophie, Countess of Wessex, were also at the castle.
The incident came before the royal's annual speech aired.
“Although it’s a time of great happiness and good cheer for many, Christmas can be hard for those who have lost loved ones. This year, especially, I understand why," she began, referring to the loss of her husband, Prince Philip, who died in April at 99 years old.
“But for me, in the months since the death of my beloved Philip, I have drawn great comfort from the warmth and affection of the many tributes to his life and work – from around the country, the Commonwealth and the world," she continued. “His sense of service, intellectual curiosity and capacity to squeeze fun out of any situation were all irrepressible. That mischievous, enquiring twinkle was as bright at the end as when I first set eyes on him."